Script to compute the number of frames for focus bracketing

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rlx Senior Member • Posts: 1,035
Script to compute the number of frames for focus bracketing

Hi. I have put together a script to compute the number of frames to set in menu entry "focus brkt" depending on the "step" setting. This is not an approximation. The script runs in Comet LUA on Android, Windows and Linux. Comet is a free software put together by Prof.Sidi Hamady.

Get the script here and copy it on an Android phone. Load the file in Comet, edit a few parameters at the top of the file an press Run. The number of frames shows up at the bottom of the screen.

Here is a stack I did with the help of the script. This is a crop. The original is 4416x2944. The locomotive is 8 cm high and is half the frame height (16 cm) at the front. I used "align_image_stack" and "enfuse". The stack was captured on the X-T3 as medium size jpeg's.

1:1 crop, 10 picture stack, 14mm, f/10, medium size jpegs from X-T3, step 7

Here is screen copy from the phone. The parameters in the picture are the one used for the above stack.

The parameters are grouped in a section on the middle of the screen. Use the editor to set the values and press Run. The result prints at the bottom. Pretty straightforward to use.

I express many thanks to the people who contributed to the following threads, Focus stacking query - any experts out there? and XT2 Focus Brackets NOT Getting to Infinity Focus. Thanks SVJIM for sharing your interpretation of the "step" parameter.

Given the complexity and variety of lenses I feel it is not clear how to measure the lens-to-subject distance. So the script provides three means of entering the data: subject-to-lens distance, subject-to-sensor distance and the frame-height.

In the stack above the subject-to-sensor distance and the frame-height return the same number of frames and the result with 10 frames just covers the locomotive. 15 frames is way too much.

As an additional check I did again computations I did before with an approximation and I now get the right number of frames if I use the new script.

Fujifilm X-T3
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